Macroevolution

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Macroevolution comprises the evolutionary processes and patterns which occur at and above the species level.<ref name="Saupe2021a">Template:Cite book</ref><ref name=":0">Template:Cite journal</ref><ref name="Gould2002a">Template:Cite book</ref> In contrast, microevolution is evolution occurring within the population(s) of a single species. In other words, microevolution is the scale of evolution that is limited to intraspecific (within-species) variation, while macroevolution extends to interspecific (between-species) variation.<ref name=":1">Template:Cite journal</ref> The evolution of new species (speciation) is an example of macroevolution. This is the common definition for 'macroevolution' used by contemporary scientists.Template:EfnTemplate:EfnTemplate:EfnTemplate:EfnTemplate:EfnTemplate:EfnTemplate:EfnTemplate:EfnTemplate:Efn However, the exact usage of the term has varied throughout history.<ref name=":1" /><ref name="DAOAL1" /><ref name=":2">Template:Cite book</ref>

Macroevolution addresses the evolution of species and higher taxonomic groups (genera, families, orders, etc) and uses evidence from phylogenetics,<ref name="Rolland2022a" /> the fossil record,<ref name="GEOL331a" /> and molecular biology to answer how different taxonomic groups exhibit different species diversity and/or morphological disparity.<ref name="Gregory2008a">Template:Cite journal</ref>

Origin and changing meaning of the term

After Charles Darwin published his book On the Origin of Species<ref>Template:Cite book</ref> in 1859, evolution was widely accepted to be real phenomenon. However, many scientists still disagreed with Darwin that natural selection was the primary mechanism to explain evolution. Prior to the modern synthesis, during the period between the 1880s to the 1930s (dubbed the 'Eclipse of Darwinism') many scientists argued in favor of alternative explanations. These included 'orthogenesis', and among its proponents was the Russian entomologist Yuri A. Filipchenko.

Filipchenko appears to have been the one who coined the term 'macroevolution' in his book Variabilität und Variation (1927).<ref name=":2" /> While introducing the concept, he claimed that the field of genetics is insufficient to explain "the origin of higher systematic units" above the species level.

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Filipchenko believed that the origin of families must require the sudden appearance of new traits which are different in greater magnitude compared to the characters required for the origin of a genus or species. However, this view is no longer consistent with contemporary understanding of evolution. Furthermore, the Linnaean ranks of 'genus' (and higher) are not real entities but arbitrary concepts.<ref name="Hendricks2014a">Template:Cite journal</ref><ref name="DAOAL1" />

The term macroevolution was adopted by Filipchenko's protégé Theodosius Dobzhansky in his book 'Genetics und the Origin of Species' (1937) and in The Material Basis of Evolution (1940) by the geneticist Richard Goldschmidt, a close friend of Filipchenko.<ref name="Adams1990a" /> Goldschmidt suggested saltational evolutionary changes<ref>Template:Cite journal</ref><ref>Template:Cite book</ref> which found a moderate revival in the hopeful monster concept of evolutionary developmental biology (or evo-devo).<ref>Template:Cite journal</ref><ref>Template:Cite book</ref> Occasionally such dramatic changes can lead to novel features that survive.

As an alternative to saltational evolution, Dobzhansky<ref>Template:Cite book</ref> suggested that the difference between macroevolution and microevolution reflects essentially a difference in time-scales, and that macroevolutionary changes were simply the sum of microevolutionary changes over geologic time. This view became broadly accepted in the middle of the last century but it has been challenged by a number of scientists who claim that microevolution is necessary but not sufficient to explain macroevolution. This is the decoupled view (see below).<ref name="Gould2002a" /><ref name=":0" /><ref name=":1" />

Microevolution vs Macroevolution

There has been considerable debate regarding the connection between microevolution and macroevolution.<ref name="Saupe2021a" />

The 'Extrapolation' view holds that macroevolution is merely cumulative microevolution.

The 'Decoupled' view holds that there are separate macroevolutionary processes that cannot be sufficiently explained by microevolutionary processes alone.<ref name="Gould2002a" /><ref>Template:Cite book</ref><ref name="Levinton2001">Template:Cite book</ref><ref name="Rolland2022a" /><ref name="Simons2002a">Template:Cite journal</ref><ref name="Erwin2001a">Template:Cite journal</ref><ref name="Adams1990a">Template:Cite journal</ref><ref name="DAOAL1" /><ref name="Moran2022a">Template:Cite web</ref>

Within microevolution, the evolutionary process of changing heritable characteristics (e.g. changes in allele frequencies) is described by population genetics, with mechanisms such as mutation, natural selection, and genetic drift,<ref name=":0" /> and speciation (e.g. sympatric and allopatric speciation), phyletic gradualism and punctuated equilibrium.<ref name="Saupe2021a" /> Macroevolution asks how higher taxonomic groups (genera, families, orders, etc) have evolved across geography and vast spans of geological time. Important questions and topics include:

Macroevolutionary processes

Speciation

Template:Main According to the modern definition, the evolutionary transition from the ancestral to the daughter species is microevolutionary, because it results from selection (or, more generally, sorting) among varying organisms. However, speciation has also a macroevolutionary aspect, because it produces the interspecific variation species selection operates on.<ref name=":1" /> Another macroevolutionary aspect of speciation is the rate at which it successfully occurs, analogous to reproductive success in microevolution.<ref name=":0" />

Speciation is the process in which populations within one species change to an extent at which they become reproductively isolated, that is, they cannot interbreed anymore. However, this classical concept has been challenged and more recently, a phylogenetic or evolutionary species concept has been adopted. Their main criteria for new species is to be diagnosable and monophyletic, that is, they form a clearly defined lineage.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Charles Darwin first discovered that speciation can be extrapolated so that species not only evolve into new species, but also into new genera, families and other groups of animals. In other words, macroevolution is reducible to microevolution through selection of traits over long periods of time.<ref>Template:Cite journal</ref> In addition, some scholars have argued that selection at the species level is important as well.<ref>Template:Cite journal</ref> The advent of genome sequencing enabled the discovery of gradual genetic changes both during speciation but also across higher taxa. For instance, the evolution of humans from ancestral primates or other mammals can be traced to numerous but individual mutations.<ref>Template:Cite journal</ref>

The diversification of terrestrial species is closely related to global climatic changes, particularly the Cenozoic alternation of warming and cooling episodes. Global analysis of terrestrial mammals supports the view that these physical environmental changes have shaped macroevolutionary patterns by promoting biome specialisation. This specialization leads to significantly higher rates of vicariance and speciation in biome specialist (stenobiomic) lineages compared to generalist lineages.<ref name="Hernández Fernández, M. et al. 2022">Template:Cite journal</ref>

Evolution of new organs and tissues

One of the main questions in evolutionary biology is how new structures evolve, such as new organs. Macroevolution is often thought to require the evolution of structures that are 'completely new'. However, fundamentally novel structures are not necessary for dramatic evolutionary change. As can be seen in vertebrate evolution, most "new" organs are actually not new—they are simply modifications of previously existing organs. For instance, the evolution of mammal diversity in the past 100 million years has not required any major innovation.<ref>Template:Cite journal</ref> All of this diversity can be explained by modification of existing organs, such as the evolution of elephant tusks from incisors. Other examples include wings (modified limbs), feathers (modified reptile scales),<ref>Template:Cite journal</ref> lungs (modified swim bladders, e.g. found in fish),<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> or even the heart (a muscularized segment of a vein).<ref>Template:Cite journal</ref>

The same concept applies to the evolution of "novel" tissues. Even fundamental tissues such as bone can evolve from combining existing proteins (collagen) with calcium phosphate (specifically, hydroxy-apatite). This probably happened when certain cells that make collagen also accumulated calcium phosphate to get a proto-bone cell.<ref>Template:Cite journal</ref>

Examples

Evolutionary faunas

A macroevolutionary benchmark study is Sepkoski's<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> work on marine animal diversity through the Phanerozoic. His iconic diagram of the numbers of marine families from the Cambrian to the Recent illustrates the successive expansion and dwindling of three "evolutionary faunas" that were characterized by differences in origination rates and carrying capacities. Long-term ecological changes and major geological events are postulated to have played crucial roles in shaping these evolutionary faunas.<ref name="Rojas2021a">Template:Cite journal</ref>

Stanley's rule

Macroevolution is driven by differences between species in origination and extinction rates. Remarkably, these two factors are generally positively correlated: taxa that have typically high diversification rates also have high extinction rates. This observation has been described first by Steven Stanley, who attributed it to a variety of ecological factors.<ref>Template:Cite book</ref> Yet, a positive correlation of origination and extinction rates is also a prediction of the Red Queen hypothesis, which postulates that evolutionary progress (increase in fitness) of any given species causes a decrease in fitness of other species, ultimately driving to extinction those species that do not adapt rapidly enough.<ref>Template:Cite journal</ref> High rates of origination must therefore correlate with high rates of extinction.<ref name=":1" /> Stanley's rule, which applies to almost all taxa and geologic ages, is therefore an indication for a dominant role of biotic interactions in macroevolution.

Evolution of multicellularity

Template:Main The evolution of multicellular organisms is one of the major breakthroughs in evolution. The first step of converting a unicellular organism into a metazoan (a multicellular organism) is to allow cells to attach to each other. This can be achieved by one or a few mutations. In fact, many bacteria form multicellular assemblies, e.g. cyanobacteria or myxobacteria. Another species of bacteria, Jeongeupia sacculi, form well-ordered sheets of cells, which ultimately develop into a bulbous structure.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Similarly, unicellular yeast cells can become multicellular by a single mutation in the ACE2 gene, which causes the cells to form a branched multicellular form.<ref>Template:Cite journal</ref>

Evolution of bat wings

The wings of bats have the same structural elements (bones) as any other five-fingered mammal (see periodicity in limb development). However, the finger bones in bats are dramatically elongated, so the question is how these bones became so long. It has been shown that certain growth factors such as bone morphogenetic proteins (specifically Bmp2) is over expressed so that it stimulates an elongation of certain bones. Genetic changes in the bat genome identified the changes that lead to this phenotype and it has been recapitulated in mice: when specific bat DNA is inserted in the mouse genome, recapitulating these mutations, the bones of mice grow longer.<ref name=":4">Template:Cite journal</ref>

Limb loss in lizards and snakes

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Limbloss in lizards can be observed in the genus Lerista which shows many intermediary steps with increasing loss of digits and toes. The species shown here, Lerista cinerea, has no digits and only 1 toe left.

Snakes evolved from lizards. Phylogenetic analysis shows that snakes are actually nested within the phylogenetic tree of lizards, demonstrating that they have a common ancestor.<ref>Template:Cite journal</ref> This split happened about 180 million years ago and several intermediary fossils are known to document the origin. In fact, limbs have been lost in numerous clades of reptiles, and there are cases of recent limb loss. For instance, the skink genus Lerista has lost limbs in multiple cases, with all possible intermediary steps, that is, there are species which have fully developed limbs, shorter limbs with 5, 4, 3, 2, 1 or no toes at all.<ref>Template:Cite journal</ref>

Human evolution

While human evolution from their primate ancestors did not require massive morphological changes, our brain has sufficiently changed to allow human consciousness and intelligence. While the latter involves relatively minor morphological changes it did result in dramatic changes to brain function.<ref>Template:Cite book</ref> Thus, macroevolution does not have to be morphological, it can also be functional.

The study of human (brain) evolution benefits from the fact that human and ape genomes are available so that the genomes of our common ancestor can be reconstructed.<ref>Template:Cite journal</ref> Even though the precise genetic mechanisms that shaped the human brain are not known, the mutations involved in human brain evolution are largely known, given that the genes expressed in the brain are relatively well understood.<ref>Template:Cite journal</ref>

Evolution of viviparity in lizards

The European Common Lizard (Zootoca vivipara) consists of populations that are egg-laying or live-bearing, demonstrating that this dramatic difference can even evolve within a species.

Most lizards are egg-laying and thus need an environment that is warm enough to incubate their eggs. However, some species have evolved viviparity, that is, they give birth to live young, as almost all mammals do. In several clades of lizards, egg-laying (oviparous) species have evolved into live-bearing ones, apparently with very little genetic change. For instance, a European common lizard, Zootoca vivipara, is viviparous throughout most of its range, but oviparous in the extreme southwest portion.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> That is, within a single species, a radical change in reproductive behavior has happened. Similar cases are known from South American lizards of the genus Liolaemus which have egg-laying species at lower altitudes, but closely related viviparous species at higher altitudes, suggesting that the switch from oviparous to viviparous reproduction does not require many genetic changes.<ref>Template:Cite journal</ref>

Research topics

Subjects studied within macroevolution include:<ref>Grinin, L., Markov, A. V., Korotayev, A. Aromorphoses in Biological and Social Evolution: Some General Rules for Biological and Social Forms of Macroevolution / Social evolution & History, vol.8, num. 2, 2009 [1]</ref>

See also

Notes

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References

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Further reading

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